Backed out 2 changesets (bug 1470163) for math failures in layout/mathml/tests/test_disabled.html on a CLOSED TREE

Backed out changeset e34a6bdac37a (bug 1470163)
Backed out changeset e2e97e7a605f (bug 1470163)

dom/base/nsDocument.cpp

@@ -1632,7 +1632,7 @@ nsDocument::~nsDocument()
         Accumulate(Telemetry::CSP_UNSAFE_EVAL_DOCUMENTS_COUNT, 1);
       }
 
-      if (MOZ_UNLIKELY(mMathMLEnabled)) {
+      if (MOZ_UNLIKELY(GetMathMLEnabled())) {
         ScalarAdd(Telemetry::ScalarID::MATHML_DOC_COUNT, 1);
       }
     }
@@ -1695,6 +1695,7 @@ nsDocument::~nsDocument()
   if (mAttrStyleSheet) {
     mAttrStyleSheet->SetOwningDocument(nullptr);
   }
+  // We don't own the mOnDemandBuiltInUASheets, so we don't need to reset them.
 
   if (mListenerManager) {
     mListenerManager->Disconnect();
@@ -1917,6 +1918,7 @@ NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN_INTERNAL(nsDocument)
 
   // Traverse all our nsCOMArrays.
   NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mStyleSheets)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mOnDemandBuiltInUASheets)
   NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mPreloadingImages)
 
   for (uint32_t i = 0; i < tmp->mFrameRequestCallbacks.Length(); ++i) {
@@ -2455,6 +2457,7 @@ nsIDocument::ResetStylesheetsToURI(nsIURI* aURI)
     // filled the style set.  (This allows us to avoid calling
     // GetStyleBackendType() too early.)
     RemoveDocStyleSheetsFromStyleSets();
+    RemoveStyleSheetsFromStyleSets(mOnDemandBuiltInUASheets, SheetType::Agent);
     RemoveStyleSheetsFromStyleSets(mAdditionalSheets[eAgentSheet], SheetType::Agent);
     RemoveStyleSheetsFromStyleSets(mAdditionalSheets[eUserSheet], SheetType::User);
     RemoveStyleSheetsFromStyleSets(mAdditionalSheets[eAuthorSheet], SheetType::Doc);
@@ -2469,6 +2472,7 @@ nsIDocument::ResetStylesheetsToURI(nsIURI* aURI)
 
   // Release all the sheets
   mStyleSheets.Clear();
+  mOnDemandBuiltInUASheets.Clear();
   for (auto& sheets : mAdditionalSheets) {
     sheets.Clear();
   }
@@ -2532,6 +2536,13 @@ nsIDocument::FillStyleSet(ServoStyleSet* aStyleSet)
     }
   }
 
+  // Iterate backwards to maintain order
+  for (StyleSheet* sheet : Reversed(mOnDemandBuiltInUASheets)) {
+    if (sheet->IsApplicable()) {
+      aStyleSet->PrependStyleSheet(SheetType::Agent, sheet);
+    }
+  }
+
   AppendSheetsToStyleSet(aStyleSet, mAdditionalSheets[eAgentSheet],
                          SheetType::Agent);
   AppendSheetsToStyleSet(aStyleSet, mAdditionalSheets[eUserSheet],
@@ -4120,6 +4131,43 @@ nsIDocument::RemoveChildNode(nsIContent* aKid, bool aNotify)
              "(maybe somebody called GetRootElement() too early?)");
 }
 
+void
+nsIDocument::EnsureOnDemandBuiltInUASheet(StyleSheet* aSheet)
+{
+  if (mOnDemandBuiltInUASheets.Contains(aSheet)) {
+    return;
+  }
+  AddOnDemandBuiltInUASheet(aSheet);
+}
+
+void
+nsIDocument::AddOnDemandBuiltInUASheet(StyleSheet* aSheet)
+{
+  MOZ_ASSERT(!mOnDemandBuiltInUASheets.Contains(aSheet));
+
+  // Prepend here so that we store the sheets in mOnDemandBuiltInUASheets in
+  // the same order that they should end up in the style set.
+  mOnDemandBuiltInUASheets.InsertElementAt(0, aSheet);
+
+  if (aSheet->IsApplicable()) {
+    // This is like |AddStyleSheetToStyleSets|, but for an agent sheet.
+    if (nsIPresShell* shell = GetShell()) {
+      // Note that prepending here is necessary to make sure that html.css etc.
+      // does not override Firefox OS/Mobile's content.css sheet.
+      //
+      // Maybe we should have an insertion point to match the order of
+      // nsDocumentViewer::CreateStyleSet though?
+      //
+      // FIXME(emilio): We probably should, randomly prepending stuff here is
+      // very prone to subtle bugs, behavior differences...
+      shell->StyleSet()->PrependStyleSheet(SheetType::Agent, aSheet);
+      shell->ApplicableStylesChanged();
+    }
+  }
+
+  NotifyStyleSheetAdded(aSheet, false);
+}
+
 void
 nsIDocument::AddStyleSheetToStyleSets(StyleSheet* aSheet)
 {
@@ -9494,6 +9542,21 @@ nsIDocument::CreateStaticClone(nsIDocShell* aCloneContainer)
           }
         }
       }
+
+      // Iterate backwards to maintain order
+      for (StyleSheet* sheet : Reversed(thisAsDoc->mOnDemandBuiltInUASheets)) {
+        if (sheet) {
+          if (sheet->IsApplicable()) {
+            RefPtr<StyleSheet> clonedSheet =
+              sheet->Clone(nullptr, nullptr, clonedDoc, nullptr);
+            NS_WARNING_ASSERTION(clonedSheet,
+                                 "Cloning a stylesheet didn't work!");
+            if (clonedSheet) {
+              clonedDoc->AddOnDemandBuiltInUASheet(clonedSheet);
+            }
+          }
+        }
+      }
     }
   }
   mCreatingStaticClone = false;
@@ -11698,6 +11761,11 @@ nsDocument::DocAddSizeOfExcludingThis(nsWindowSizes& aWindowSizes) const
   aWindowSizes.mLayoutStyleSheetsSize +=
     SizeOfOwnedSheetArrayExcludingThis(mStyleSheets,
                                        aWindowSizes.mState.mMallocSizeOf);
+  // Note that we do not own the sheets pointed to by mOnDemandBuiltInUASheets
+  // (the nsLayoutStyleSheetCache singleton does).
+  aWindowSizes.mLayoutStyleSheetsSize +=
+    mOnDemandBuiltInUASheets.ShallowSizeOfExcludingThis(
+      aWindowSizes.mState.mMallocSizeOf);
   for (auto& sheetArray : mAdditionalSheets) {
     aWindowSizes.mLayoutStyleSheetsSize +=
       SizeOfOwnedSheetArrayExcludingThis(sheetArray,

dom/base/nsIDocument.h

@@ -836,6 +836,14 @@ public:
     mBidiEnabled = true;
   }
 
+  /**
+   * Check if the document contains (or has contained) any MathML elements.
+   */
+  bool GetMathMLEnabled() const
+  {
+    return mMathMLEnabled;
+  }
+
   void SetMathMLEnabled()
   {
     mMathMLEnabled = true;
@@ -1460,6 +1468,28 @@ public:
    * Style sheets are ordered, most significant last.
    */
 
+  /**
+   * These exists to allow us to on-demand load user-agent style sheets that
+   * would otherwise be loaded by nsDocumentViewer::CreateStyleSet. This allows
+   * us to keep the memory used by a document's rule cascade data (the stuff in
+   * its nsStyleSet's nsCSSRuleProcessors) - which can be considerable - lower
+   * than it would be if we loaded all built-in user-agent style sheets up
+   * front.
+   *
+   * By "built-in" user-agent style sheets we mean the user-agent style sheets
+   * that gecko itself supplies (such as html.css and svg.css) as opposed to
+   * user-agent level style sheets inserted by add-ons or the like.
+   *
+   * This function prepends the given style sheet to the document's style set
+   * in order to make sure that it does not override user-agent style sheets
+   * supplied by add-ons or by the app (Firefox OS or Firefox Mobile, for
+   * example), since their sheets should override built-in sheets.
+   *
+   * TODO We can get rid of the whole concept of delayed loading if we fix
+   * bug 77999.
+   */
+  void EnsureOnDemandBuiltInUASheet(mozilla::StyleSheet* aSheet);
+
   mozilla::dom::StyleSheetList* StyleSheets()
   {
     return &DocumentOrShadowRoot::EnsureDOMStyleSheets();
@@ -3586,6 +3616,7 @@ protected:
 
   void UpdateDocumentStates(mozilla::EventStates);
 
+  void AddOnDemandBuiltInUASheet(mozilla::StyleSheet* aSheet);
   void RemoveDocStyleSheetsFromStyleSets();
   void RemoveStyleSheetsFromStyleSets(
       const nsTArray<RefPtr<mozilla::StyleSheet>>& aSheets,
@@ -4387,6 +4418,7 @@ protected:
   nsCOMPtr<nsIRunnable> mMaybeEndOutermostXBLUpdateRunner;
   nsCOMPtr<nsIRequest> mOnloadBlocker;
 
+  nsTArray<RefPtr<mozilla::StyleSheet>> mOnDemandBuiltInUASheets;
   nsTArray<RefPtr<mozilla::StyleSheet>> mAdditionalSheets[AdditionalSheetTypeCount];
 
   // Member to store out last-selected stylesheet set.

dom/mathml/nsMathMLElement.cpp

@@ -106,9 +106,25 @@ nsMathMLElement::BindToTree(nsIDocument* aDocument, nsIContent* aParent,
     aDocument->RegisterPendingLinkUpdate(this);
   }
 
-  // Set the bit in the document for telemetry.
-  if (nsIDocument* doc = GetComposedDoc()) {
-    doc->SetMathMLEnabled();
+  nsIDocument* doc = GetComposedDoc();
+  if (doc) {
+    if (!doc->GetMathMLEnabled()) {
+      // Enable MathML and setup the style sheet during binding, not element
+      // construction, because we could move a MathML element from the document
+      // that created it to another document.
+      auto cache = nsLayoutStylesheetCache::Singleton();
+      doc->SetMathMLEnabled();
+      doc->EnsureOnDemandBuiltInUASheet(cache->MathMLSheet());
+
+      // Rebuild style data for the presshell, because style system
+      // optimizations may have taken place assuming MathML was disabled.
+      // (See nsRuleNode::CheckSpecifiedProperties.)
+      RefPtr<nsPresContext> presContext = doc->GetPresContext();
+      if (presContext) {
+        presContext->
+          PostRebuildAllStyleDataEvent(nsChangeHint(0), eRestyle_Subtree);
+      }
+    }
   }
 
   return rv;

layout/base/nsDocumentViewer.cpp

@@ -2512,12 +2512,9 @@ nsDocumentViewer::CreateStyleSet(nsIDocument* aDocument)
     styleSet->PrependStyleSheet(SheetType::Agent, sheet);
   }
 
-  if (MOZ_LIKELY(mDocument->NodeInfoManager()->SVGEnabled())) {
-    styleSet->PrependStyleSheet(SheetType::Agent, cache->SVGSheet());
-  }
-
-  if (MOZ_LIKELY(mDocument->NodeInfoManager()->MathMLEnabled())) {
-    styleSet->PrependStyleSheet(SheetType::Agent, cache->MathMLSheet());
+  sheet = cache->SVGSheet();
+  if (sheet) {
+    styleSet->PrependStyleSheet(SheetType::Agent, sheet);
   }
 
   styleSet->PrependStyleSheet(SheetType::Agent, cache->UASheet());